Contact diode



May 22, 1956 R. LOOSJES CONTACT DIODE Filed Jan. 27, 1953 INVENTOR ROBERIIoo/Sa United States Patent Oiice CONTACT DIODE Robert Loosjes, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application January 27, 1953, Serial No. 333,416

Claims priority, application Netherlands March 1li, 1952 3 Claims. (Cl. 313-235) The invention relates to contact diodes, that is to say to diodes the anode of which is in direct contact with the oxide layer of the cathode.

Contact diodes have been suggested before and have the advantage that the voltage drop in the conducting phase is comparatively low, while permitting a comparatively high tension to be maintained in the other direction. In the known contact diodes anode and cathode are constituted by short cylindrical sleeves open at the back. The thermal eiciency is poor and to ensure a permanent satisfactory contact between the anode and the oxide layer the electrodes have to be forcibly held against each other which presents diiculty from the mechanical point of view.

The object of the invention is to provide an improvement upon the known contact diodes, so as to ensure satisfactory thermal efficiency and further to reduce the voltage drop in the conductive direction.

A contact diode according to the invention comprises a cylindrical or slightly conical electrode system having the cathode as the inner electrode. The anode may be realized as a solid shell and in this case a slightly conical shape assists in the arrangement of the anode to surround the oxide-coated cathode. To ensure satisfactory contact between the anode and the oxide layer and a maximum surface area if the anode is a solid cylindrical shell or even if it has a slightly conical shape, the anode may have pressed grooves in it after assembly so as to ensure more satisfactory engagement with the oxide layer. The grooves may follow one system of lines or two systems of intersecting lines.

As an alternative, satisfactory contact between the anode and the oxide layer is obtained, when the anode is constituted by a system of wires arranged closely adjacent each other on the oxide layer, for example wires parallel to the axis of the cylindrical anode or a wire wound helically in one or more turns. To maintain the temperature of the anode at a low value in order to prevent any passage of current in the wrong direction, crosswires may be welded on to the wires constituting the anode, so as appreciably to improve the radiation.

Since a contact diode is not necessarily arranged in a vacuum, but may be accommodated in an inert gas atmosphere or some other non-corroding gas, cooling tins may be used instead of cross-wires.

Particularly if the anodes are constituted by wires, but also in the case of a solid anode it is preferable that at the surface which is in contact with the oxide layer the anode should be of gold, silver, thorium or some other 2,747,127 Patented May 22, 1956 material on which alkaline-earth metal oxides have a poor emission.

The invention will now be described with reference to the accompanying drawing, given by way of example, in which:

Figure 1 is a sectional view of a contact diode cornprising electrodes of slightly conical shape.

Figures 2A and 2B are elevations of cylindrical contact diodes comprising grooves of diifering forms.

Figures 3A and 3B and 4A and 4B are Sectional views of contact diodes comprising anodes made of wire.

Referring now to Fig. l, a slightly conical nickel body l, 0.1 mm. thick, is coated with a barium strontium oxide layer 2, 2.70 microns thick, and thus serves as a cathode. A slightly conical nickel anode 3 is coated internally with a layer of gold 4 some few microns thick. An electrically heated helix is designated 5. In the case of a cathode diameter of 2 mm., a length of the sprayed layer of 20 mm. and a heating energy of 2.5 watts the resistance in the conductive direction was 2O ohms at a current of approximately ma. In the opposite direction the resistance was 10,000 ohms and in this direction a potential of 50 volts could be resisted without breakdown of the oxide layer.

In Figure 2A, the anode 6 has grooves impressed on it according to helical .lines 7, and in Fig. 2B according to left-handed and right-handed helical lines 8 and 9.

In Figure 3A the electrically heated helix is similarly designated 5, the nickel cathode cylinder 10, the oxide layer 11. The oxide layer 11 has a thorium wire 12 helically wound on it. The helically wound thorium wire 12 has welded to it tungsten rods 13, as grid supports are welded to grid wires. Figure 3B shows a construction in which tantalum cooling tins 14 are welded to the thorium wire 12.

Figures 4A and 4B are cross-sectional views taken at right angles to the axis of Figures 3A and 3B.

What I claim is:

l. A contact diode comprising a hollow substantially cylindrical cathode electrode, an oxide coating on the outer surface of said cathode, and an anode mounted on and surrounding and abutting the oxide coating on the cathode, said anode having an inner surface abutting said oxide coating constituted of an emission-reducing material selected from the group consisting of gold, silver and thorium.

2. A contact diode as set forth in claim l wherein the cathode electrode is constituted of nickel, and the oxide coating is an alkaline earth metal oxide coating.

3. A contact diode as set forth in claim 1 wherein the anode is a solid metal shell surrounding and abutting the oxide coating, said anode being provided with a plurality of grooves therein.

References Cited inthe le of this patent UNITED STATES PATENTS 882,218 Thomas Mar. 17, 1908 1,839,899 Slepian Ian. 5, 1932 2,601,024 Jacobs et al. June 17, 1952 FOREIGN PATENTS 115,700 Great Britain May 2l, 1918 

1. A CONTACT DIODE COMPRISING A HOLLOW SUBSTANTIALLY CYLINDRICAL CATHODE ELECTRODE, AN OXIDE COATING ON THE OUTER SURFACE OF SAID CATHODE, AND AN ANODE MOUNTED ON AND SURROUNDING AND ABUTTING THE OXIDE COATING ON THE CATHODE, SAID ANODE HAVING AN INNER SURFACE ABUTING SAID OXIDE COATING CONSTITUTED OF AN EMISSION-REDUCING MATERIAL SELECTED FROM THE GROUP CONSISTING OF GOLD, SILVER AND THORIUM. 